Respiration is the process during which simple carbohydrates, like glucose, break down into simpler substances and liberate carbon dioxide and energy. The compound used, or oxidized, during respiration is called a respiratory substrate. Carbohydrates, fats, and proteins are examples of respiratory substrates, and carbohydrates are the preferred respiratory substrate among them. Respiration produces a great deal of energy that is needed by plants to grow and stay healthy. Excess sugars produced by photosynthesis that are not needed for respiration and growth are stored as starch which can then be converted back to sugars when needed during periods of low light. The rate of respiration can be measured in terms of gas exchange, that is, consumption of the respiratory substrate oxygen, or evolution of carbon dioxide.
This video explains how to study the rate of respiration in germinating seeds having different substances such as wheat (carbohydrates), mustard (fats) and bean (proteins).